This invention relates to a communications network and, in particular, to a communications network whose operation is based on encrypted messages between terminals.
Recently, together with the development of electronic technology there have been developments in systems such as home banking and shopping, and office banking systems using advanced communications systems. A vital concern in regards to a communications network system for money transactions is the guarantee of secrecy and security of these transactions. It is necessary to increase the verifiability of the transactor or communication message which is transmitted and received between transactors through the communication network.
The classical types of irregularities that can occur in the transmission of transactions or messages are as follows.
(1) False reports. A sender reports not sending to the receiver although in actuality a transmission was made, or the sender reports sending although no transmission was made.
(2) Forgery of documents. Receiver rewrites communication message that has been recorded on the receiving side, or makes a forged communication message.
These kinds of irregularities are the basis of embezzlement.
In a prior art system, in order to prevent these irregularities, an enciphering program such as DES (Data Encription Standard) is stored in each network terminal to prevent the forging of communication messages. This means that an enciphering/deciphering circuit is provided in each terminal and that a sender, using his own key, enciphers a message according to this enciphering program. The enciphered message is transmitted to a receiver terminal through a communication network. On the receiver side, the received enciphered message is recorded and deciphered in the deciphering circuit using a key word which is stored in a key memory and peculiar to the sender. Accordingly, assuming that the key word stored in the key memory on the receiver side has not leaked to the outside, and that the receiver has not forged the message, there is no one other than the sender who knows the key word who can make the recorded enciphered message. Accordingly, the verifiability of the enciphered message stored on the receiver side is very high. This kind of a system where no one other than a specific person can prepare the message is amenable to the use of digital signatures.
In general, however, it is impossible to preclude irregularities by the receiver, who knows the contents of the key memory and may, with the use of a computer, prepare the enciphering program and, with the special key word of a sender, prepare a false enciphered message. Consequently, with this kind of communications network, it is impossible to completely prevent irregularities from being prevented by both sides, making it difficult to ensure the secrecy and security of the transactions conducted over the network.